Agriculture

An important part of maximizing the accuracy of COWBYTES ration recommendations is ensuring input parameters are as accurate as possible. The request to enter "Slaughter/Mature Weight" for feeder calves seems to cause some confusion especially when preparing background rations. Slaughter Weight refers to the weight at which an animal reaches the desired grade. Mature Weight is the weight at 5 years of age at a condition score of 3(Canadian BCS scale). This Slaughter/Mature Weight is compared against a reference weight. It assumes that cattle have a similar body composition at the same degree of maturity. The NRC medium-frame steer is used as the reference animal for the various weights at which cattle will grade A, AA, or AAA on the Canadian marbling system. COWBYTES uses the starting weight, the final slaughter/mature weight and the estimated marbling score to calculate what is called an equivalent body weight. This is then used to calculate the NEG and average daily gain. It is important to estimate the Slaughter/Mature Weight as close to reality as possible because of the effect on requirements. For example, feeder steers (A,B) have equal start weights of 704 lbs. but different slaughter weights, 1320 and 1056, respectively. COWBYTES will calculate equivalent body weights of 562 lbs. (feeder A) and 702 lbs. (feeder B). If both feeders receive the same net energy for gain (5mcal/day) feeder A will gain just over 3 lbs. while steer B will gain only 2.6 lbs. For more information refer to the Help Screen in COWBYTES and Chapter 3 of“Nutrient Requirements of Beef Cattle”, NRC,1996.

The following table provides guidelines for target ADG and slaughter weights for different frame sizes of steers and heifers destined for American and Canadian markets (Source: Dr. J. McKinnon, University of Saskatchewan).